In many manufacturing settings there is a need to dispose of waste gas streams. While the simplest and least expensive disposal method is to exhaust the gas stream into the ambient atmosphere, such a disposal method may cause harm to the environment, and may violate federal, state or local pollution control laws in those instances where the waste gas stream contains organic chemicals. It has therefore become common practice to pass waste gas streams through a scrubber, in order to remove certain organic components from the gas stream and allow the gas stream to be safely exhausted into the atmosphere.
One device commonly used for removal of organic chemicals from a waste gas stream is a thermal oxidizer. In a typical thermal oxidizer, the waste gas stream is combined with an oxygen-containing gas stream, e.g., air, and then passed through a flame produced by burning a combustible substance, e.g., natural gas. This process oxidizes the organic chemicals and converts them into carbon dioxide and water. The thermal oxidizer thus converts certain organic chemicals into environmentally harmless chemicals that may be safely exhausted into the atmosphere. In many modern manufacturing plants, thermal oxidizers are permanently installed in gas exhaust ducts.
While in theory and preferred practice, a thermal oxidizer can oxidize all or substantially all of the undesirable organic chemicals in a waste gas stream, in actual practice the thermal oxidizer may not be working as expected or desired. For example, the incoming waste gas stream may be flowing too quickly to allow complete oxidation of all the component organic chemicals, or there may be inadequate contact between the waste gas stream and the flame. It is therefore desirable, and often required under pollution control laws, to periodically test the efficiency of a thermal oxidizer.
To calculate the efficiency of a thermal oxidizer, one needs to determine the extent to which incoming organic chemicals are oxidized to carbon dioxide and water. Thus, one needs to know the mass flow rate of the organic chemicals entering the thermal oxidizer. Commonly, and according to procedures set forth by the United States Environmental Protection Agency (EPA), a test chemical is introduced into a waste gas stream at a point prior to the waste gas stream being subjected to oxidization in the thermal oxidizer, i.e., upstream of the thermal oxidizer. The test chemical should be introduced to the gas stream at a known and controllable mass flow rate, which is assumed to be the mass flow rate at which the test chemical enters the thermal oxidizer.
When the test chemical is a gas, one can reasonably assume that the measured rate at which the test chemical enters the gas stream, on the inlet side of a thermal oxidizer, is equal to the actual rate at which the test chemical enters the thermal oxidizer. However, when the test chemical is a liquid, the same assumption may not hold true. For example, according to the prior art, a liquid test chemical may be injected into the inlet waste gas stream by way of an atomizer placed inside the duct that directs a waste gas stream into the thermal oxidizer. This is known as the aspirator technique of introducing liquid test chemical into a waste gas stream. While it is easy to monitor the rate at which the liquid test chemical is sent through the atomizer, one may find, after the efficiency test is completed, that the duct(s) between the atomizer and the thermal oxidizer is covered by droplets, if not pools, of the liquid test chemical. In this situation, one cannot use the measured rate that liquid test chemical is sent into the duct as a basis for determining the efficiency of the oxidizer, because that measured rate is clearly not equal to, and has no known correlation with, the rate that test chemical actually enters the oxidizer.
Based on the foregoing, it can be seen that there is a pressing need in the art for an apparatus and method for reliably introducing a known and controlled rate of liquid test chemical into a thermal oxidizer, so that the efficiency of the thermal oxidizer can be accurately determined.